Inkjet printheads for aqueous inks use multiple strategies for mitigating issues caused by ink drying within individual jet orifices. Inkjet printheads typically rely upon a stack of plates referred to as a jet stack, the final plate of which has an array of nozzles. When an inkjet printhead is latent, water or other volatiles evaporate from the ink. Evaporation may happen even during shorter periods of latency, such as less than an hour. Evaporation of water and other volatiles results in an increase in ink viscosity, which causes ink drops to eject with a lower velocity, less drop volume, or, in some cases, not eject at all.
One common technique to counteract the increase in ink viscosity is to purge the inkjet printhead with fresh ink prior to printing. However, this requires time and fresh ink to accomplish, and results in a waste of ink. After a long period of latency, such as more than an hour, purging is often needed, but purging is not a preferred method for shorter periods of latency because of the amount of time and ink required for purging.
Other techniques may use maintenance ink drops, also referred to as sneezing, to keep fresh ink in the inkjet printhead. However, sneezing requires print media to be available to receive the ink drops. Thus, sneezing is useful during a print job, but not between print jobs since there is no print media present.
Finally, non-firing waveforms may be applied to the inkjet. Non-firing waveforms are not strong enough to result in an ink drop and help mix the dry ink near the nozzle with fresher ink in the rest of the inkjet printhead. Mixing the dry ink with fresher ink by using non-firing waveforms helps with the robustness of the first ink drops after a period of latency. However, the effectiveness of the non-firing waveforms is reduced when the ink drops are very small, such as less than 3 pl. When the ink drops are very small, the first ink drops will either still fail to eject or will be noticeably lighter.
What is needed is an improvement in the robustness of the first ink drops ejected after a period of latency, when the latency period is short enough that a purge is not needed, maintenance ink drops are not practical, and/or the drop volume is small (e.g. less than 3 picoliters (pl)).